1. Technical Field
The invention relates to chairs, particularly to flexible tilting support to a chair back.
2. Related Art
Rearward tilting chair backs helps users to obtain comfortable sitting. But such rearward tilting must be flexible supported to avoid flaccidness. In addition, the flexibility of rearward tilting cannot be hard enough to cause difficulties of operation and use. However, control of the flexibility is a considerably difficult issue for furniture industry.
FIG. 1 shows an existing flexible support and flexibility adjustment structure. It uses an end of an adjusting rod 60 to screw up to a driven block 62. A transmission rod 63 is arranged on a base 61. The transmission rod 63 is axially connected to the driven block 62 through a link set 65. A spring 64 is put around the transmission rod 63. The other end of the base 61 is provided with a driving member 66 connected to the chair back. An end of the spring 64 is stopped by an end of the driving member 66. When the chair back is tilted rearward, the driving member 66 directly compresses the spring 64 to obtain flexible support. Additionally, by the connective move of the driven block 62 and the transmission rod 63, the transmission rod 63 shifts to change elasticity of the spring 64 to obtain desired flexibility adjustment.
In such a structure, the chair back is flexibly supported by the driving member 66 directly exerting a force onto the spring 64. However, the distance between the effort point and spring 64 is short in length, so a larger force is required to compress the spring 64. It really causes a difficulty in operation.
Moreover, the link set 65 has to change the force direction between the adjusting rod 60 and the transmission rod 63. If the link set 65 jams or has other rotational resistance, then the whole structure will malfunction. Also, the link set 65 transfers the force to the transmission rod 63 through one side, so unbalance is easy to occur to cause deflection of shift of the transmission rod 63 and structural damage.